Incidents involving active shooters which include shootings in a confined environment, such as a school or classroom, has been increasing yearly and the statistics associated with them are that “a life is lost every 15 seconds.” This translates into the first responders protocol to “locate and engage” the shooter as quickly as possible. This implies that to save lives detection and location of the shooter is the most critical information for first responders.
Gunshots are significant energy events having both large audio decibel levels and long signal durations of up to half a second. Both of these attributes are enhanced by reflections from the walls and the floor, which increases the signal duration by the associated delayed arrival of the signal multi-paths. The large amounts of energy released by a weapon discharge also generate significant nonlinearities which result in the generation of higher harmonics.
Current gunshot detection systems are designed for deployment in an open-air environment, such as a street, battlefield, ocean, or wilderness region such as a rain forest. In open environment, there is infinite space, and the sound wave of a gunshot is, to first approximation, free to propagate without significant reflections from nearby boundaries. In this environment, features of the shock wave or shock front (e.g., rise time, rise slope) produced by the discharge can be analyzed.
In a confined or substantially closed environment, there are several complications when a firearm is discharged. There is the sound of the gunshot itself, sound of the bullet impacting a wall or target close to the gunshot, and reflections off the wall, ceiling, or floor. In this setting, the shock wave or shock front from the explosion moves at a certain speed and is distorted due to multiple reflections. So using the shock front in a confined space such as a room, as opposed to an open environment, would require an extremely difficult analysis that would necessitate incorporation of the complex boundary geometry particular to the room in which the weapon was discharged.
What is needed is a sensor system which can detect and analyze the gunshot in a confined environment to distinguish between threats and non-threats, determine the type(s) of weapons involved and the number of rounds fired, and doing so without requiring room-specific signal analysis.